1. A machine tool comprising:a rotary table adapted to support an object to be machined and which is capable of being rotated; and
a clamp mechanism adapted to clamp the rotary table in a manner so that the rotary table does not rotate;
wherein a clamping operation by the clamp mechanism is started after a standby time has elapsed from completion of indexing of the rotary table;
the machine tool further comprising:
a positional deviation calculating unit adapted to calculate a positional deviation of the rotary table when the clamping operation by the clamp mechanism is completed; and
a standby time changing unit adapted to shorten the standby time in the case that an absolute value of the positional deviation is less than a threshold value, and to lengthen the standby time in the case that the absolute value of the positional deviation is greater than the threshold value,
wherein the standby time is set to be, as an initial value, longer than a time period required for overshooting to converge.